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What are Positive Displacement Blowers?

A positive displacement blower conveys gas or air from the upper inlet port into the stage using two parallel rotary pistons. These are mounted within a housing also called a conveying chamber(s). The pistons rotate in opposite directions and facilitate gas or air conveyance from the top to the bottom. Positive displacement blowers are also known as PD blowers or rotary air blowers.

How do Positive Displacement Blowers work?

There are two types of positive displacement blowers; lobe and screw.


Lobe Positive Displacement Blower

A positive displacement lobe blower is a machine that conveys a relatively constant volume of gas from the inlet to the discharge point. It follows the isochoric compression principle, also known as external compression.

In this principle, the medium (gas or air) is forced from an atmospheric condition into a system with a given resistance (back pressure) to achieve the relevant pressure increase. For this reason, positive displacement lobe blowers are not considered compressors. The amount of gas the machine handles is fixed by the configuration of its casing and rotating parts.

Screw Positive Displacement Blower

In a positive displacement screw blower, the rotors turn in opposite directions to maintain precise alignment by means of timing. When the rotors mesh, they form a series of working chambers between the rotors and the casing wall.

The gas is sucked from the intake side (suction) and trapped between the rotors and the casing (radially) and the cover (axially). It is then transported to the compression side (discharge) where the working chamber shrinks, and the air or gas is compressed. The internal compression leads to a supply of steady, non-pulsating air flow. This minimises vibration and maintenance to maximizing the lifespan of the blower.

Robuschi’s Range of Positive Displacement Blowers

Robuschi offers both types of positive displacement blowers. The rotary lobe (capacity up to 25,000 m³/h) and the screw (capacity up to 10.100 m³/h) meet the various needs of customers and their wide range of applications.

The rotary lobe blower accommodates the renowned RBS airend. This rotary lobe blower provides an excellent solution for oil-free conveyance of air and neutral gases. It is equipped with a low-pulse system that reduces the residual pressure pulsation of the conveyed gas below 2% of the operating pressure.


The screw blower range uses the CDL and RSW state-of-the-art, patented airends (depending on sizes).


Robuschi positive displacement blower range offers a sturdy design for continuous duty and robust operation, and a long service life and efficient performance.

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